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  1. Were the forces of nature combined in one unifying force at the time of the Big Bang?

  2. By which symmetry is this unification governed?

  3. Are there any evidence for such unification of forces?

  4. Has ever been published Theory or experiment in this issue? (Even original researches or unpublished theories. Anything that you can start with.)

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Dear Baner, concerning your update, yours is a formalism of classical mechanics that was most recently used for state-of-the-art theories more than 100 years ago, in 1905. It's just obsolete today and it makes no sense to try to discuss unification of forces using the formalism of classical physics. One needs at least "quantum field theory" to even discuss whether basic forces of Nature as we understand them today may unify and how. $F=ma+\Delta F$ won't do. – Luboš Motl Dec 14 '12 at 17:36
This is Einstein's theory of relativity and still applies, even in the LHC accelerator – anon Dec 14 '12 at 17:42
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@baner Lubos Motl is right, your edit makes no sense. It is meaningless to discuss the unification of the forces of nature only in the classical limit. I am not sure if you know what you are asking about in your question ... You are not even able to fetch the right tags. – Dilaton Dec 14 '12 at 17:47

1 Answer

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The unifying theories of the three non-gravitational forces are known as GUT, Grand Unified Theories. The only known consistent unification of all forces including gravity (plus the known matter species) is string/M-theory.

The relevant energies or temperatures where the unification become crystal clear are very high – de facto experimentally inaccessible – which is why the new aspects of these theories were only relevant shortly after the Big Bang and why it seems impossible to make "direct experiment tests" of any grand unifying theories or more ambitious ones. However, there are some general possible experimental discoveries that, if they would emerge, would be strong arguments in favor of the validity of the frameworks.

But there exists a powerful body of theoretical evidence that string theory is right and it seems more likely than not that grand unification is realized in Nature, too (string theory admits models without grand unification of the 3 non-gravitational forces in the usual sense).

There are many isolated detailed grand unified models and we don't know which is right. Analogously, string theory has many solutions how the empty space may look – although they're connected within the string theory framework – and no one quite knows which theory/solution is the relevant one for the Universe around us.

I am afraid it makes no sense to give you more details about the theories because it seems that you have never heard anything about them and too much data would just confuse you. The literature on the subjects is huge, tens of thousands of papers, and one can't really summarize and there's no point of doing so. There are also dozens or hundreds of popular books on the subject. You would have to ask more specific questions.

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Motl's claim that string/M-theory is "the only known consistent unification of all forces including gravity" is an exaggeration, because nobody has shown such thing. Moreover the internal consistency of string/M-theory has not been shown but is only "widely believed" as the second link states. – juanrga Dec 14 '12 at 16:31
i'm looking for a new theory – user17389 Dec 14 '12 at 17:15
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I just need to write that the 3 comments above are not a part of my answer and I can't endorse any of them because none of them is valid. – Luboš Motl Dec 14 '12 at 17:25
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I dont agree with juanrga either. These comments should be removed since they add neither to the topic of the question nor the the answer anything meaningful. They are rather distractive. – Dilaton Dec 14 '12 at 17:40
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@bane you can watch this video of Prof. Susskind. Therein he explains how the electromagnetic, the weak and the strong forces can be unified into a larger SU(5) GUT structure. If you need to see the group theory watch the lecture before too. However, this SU(5) GUT does not contain gravity. – Dilaton Dec 14 '12 at 21:43
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